Density and Viscosity Measurements for Binary Mixtures of 1‑Ethyl-3-methylimidazolium Tetrafluoroborate ([Emim][BF₄]) with Dimethylacetamide, Dimethylformamide, and Dimethyl Sulfoxide

The density and viscosity data of three binary liquid mixtures containing the ionic liquid (IL) 1-ethyl-3-methylimidazolium tetrafluoroborate and organic solvents, dimethylacetamide (DMAC), dimethylformamide (DMF), and dimethyl sulfoxide (DMSO) were obtained under atmospheric pressure, at temperatures of 303.15 to 333.15 K over the entire composition range. A vibrating-tube digital density meter and a capillary viscometer were used for density and viscosity measurements, respectively. Excess molar volumes (<i>V</i>^E) and viscosity deviations (Δη) for the binary mixture system were calculated from the experimental data and were satisfactorily fitted with the Redlich–Kister equation. Adding DMAC, DMF, and DMSO led to negative values of <i>V</i>^E and Δη. This finding revealed that the packing of the constituents was more efficient, and the anion–cation interaction of IL was decreased in the binary liquid mixtures. The sequences of <i>V</i>^E and Δη for the three binary liquid mixtures in this study are also discussed using intermolecular interactions

Molecular Dynamics Study on the Equilibrium and Kinetic Properties of Tetrahydrofuran Clathrate Hydrates

Tetrahydrofuran (THF) is an effective promoter of methane hydrates, and itself with water can form clathrate hydrates even without the presence of methane gas. In this work, the stability limit and kinetic properties of THF hydrates were simulated using molecular dynamics (MD) simulations. The change in dissociation temperature of THF hydrates with pressure and concentration of THF in the aqueous phase were well reproduced with MD simulations. The rate of growth of THF hydrates is found to exhibit a maximum value when the liquid-phase THF concentration is about 0.3–0.8 times (depending on temperature) of the THF concentration in the hydrate phase. The existence of some optimal growth concentration explains the preferred lateral growth in experiments. The maximum growth rate is a result of two competing effects: the adsorption of THF molecules to the growing interface, which is the limiting step at low THF concentrations, and the desorption/rearrangement of THF molecules at the interface, limiting step at high THF concentrations. The large cages of structure II (sII) hydrate are fully occupied by THF molecules, regardless of the THF concentration in the aqueous phase, implying a strong stabilization effect of THF molecules to the cage structures of sII hydrates

Molecular Dynamics Study on the Growth Mechanism of Methane plus Tetrahydrofuran Mixed Hydrates

Molecular dynamics (MD) simulations are performed to analyze the dominating factors for the growth of CH₄ + THF mixed hydrates, and the results are compared with the growth of single guest CH₄ and THF hydrates. While CH₄ hydrate has a type I crystalline structure, the presence of THF in the aqueous phase results in the growth the type II structure hydrate. Compared to THF hydrates, the presence of CH₄ in the system enhances the dissociation temperature. The growth rate of CH₄ + THF mixed exhibits a maximum value at about 290 K at 10 MPa. The growth rate is found to be determined by two competing factors: (1) the adsorption of CH₄ at the solid–liquid interface, which is enhanced with decreasing temperature, and (2) the migration of THF to the proper site at the interface, which is enhanced with increasing temperature. Above 290 K, which is about 10 K higher than the dissociation temperature of pure THF hydrate, the growth of cage can proceed only when a sufficient amount of CH₄ is adsorbed at the interface. The growth rate is dominated by the uptake of CH₄ at the interface, as in the case of pure CH₄ hydrate. Below 290 K, the growth is not much affected by the presence of CH₄. Instead, the growth rate is determined by the rearrangement of THF molecules at the interface, as in the case of pure THF hydrate

Effect of Intraoperative High-Dose Remifentanil on Postoperative Pain: A Prospective, Double Blind, Randomized Clinical Trial

<div><p>Background</p><p>Remifentanil, an ultra-short-acting opioid, is widely used for pain control during surgery. However, regular dose (RD) remifentanil exacerbates postoperative pain in a dose-dependent manner. Recent studies suggest that high-dose (HD) remifentanil offers sustained analgesia in experimental studies. We thus hypothesized that intraoperative administration of high-dose remifentanil may attenuate postoperative pain.</p><p>Methods</p><p>In this prospective, randomized, double blind, controlled clinical study, sixty patients undergoing thyroidectomy (18–60 years-of-age) received an intraoperative infusion of 0.2 (RD group) or 1.2 μg kg⁻¹min⁻¹ (HD group) remifentanil during thyroidectomy. A visual analogue scale (VAS) was used to measure pain intensity. Mechanical pain threshold on the forearm was assessed using von Frey filaments before surgery (baseline), 2 h postoperatively and 18–24 h postoperatively. The primary outcome was to compare the difference of VAS score at different time points after operation and morphine consumption 24 h postoperatively between RD and HD groups. The second outcome was to compare the difference of mechanical pain thresholds in the forearm postoperatively between RD and the HD groups.</p><p>Results</p><p>VAS scores were lower 30 min postoperatively in the HD group (1.29±1.67, 95% CI 0.64–1.94) compared with the RD group (2.21±1.67, 95% CI 1.57–2.84) (t = 3.427, p = 0.0043, RD group vs. HD group). Postoperative morphine consumption was much lower in the HD group compared with the RD group (1.27±1.88 mg vs. 0.35±1.25 mg, p = 0.033). In both groups, mechanical pain threshold was decreased 18–24 h postoperatively (2.93±0.209 Ln(g) vs. 3.454±2.072 Ln(g), p = 0.032 in RD group; 2.910±0.196 Ln(g) vs. 3.621±0.198 Ln(g), p = 0.006 in HD group, 18–24 h postoperatively vs baseline).</p><p>Conclusions</p><p>Intraoperative administration of high-dose remifentanil decreased VAS scores and morphine consumption postoperatively. Thus, modulation of intraoperative opiates may be a simple and effective method of postoperative pain management.</p><p>Trial Registration</p><p>This trial is registered in <a href="http://www.ClinicalTrials.gov" target="_blank">ClinicalTrials.gov</a>, with the Name: Effect of Higher Doses of Remifentanil on Postoperative Pain in Patients Undergoing Thyroidectomy, and ID number: <a href="http://clinicaltrials.gov/ct2/show/NCT01761149" target="_blank">NCT01761149</a>.</p></div

Trial profile.

<p>Trial profile.</p

Time course of mechanical pain threshold in the forearm after surgery.

<p>Note the significantly decreased mechanical pain threshold at 2–24 h postoperatively compared to baseline in RD group (p<0.05, Two-way ANOVA analysis followed by Bonferroni’s <i>post hoc</i> test). In HD group, the mechanical pain threshold is also significantly decreased at 18–24 h postoperatively when compared with baseline (p<0.01, Two-way ANOVA analysis followed by Bonferroni’s <i>post hoc</i> test). *p<0.05, post-2 h or 18–24 h postoperatively <i>vs</i> baseline.</p

Patients’ anesthetic characteristics.

<p>Values are presented as mean±SD, or the number of patients. PONV, postoperative nausea or vomiting.</p

Hemodynamic data and BIS scales.

<p>Values are expressed as mean±SD. RD: regular dose remifentanil group; HD: high-dose remifentanil group; HR: heart rate; SBP: systolic blood pressure; DBP: diastolic blood pressure; MAP: mean arterial pressure; BIS: bispectral index; Aft indu: 1 min after induction; 5 min aft and 10 min aft: 5 min and 10 min after induction, respectively; End oper: End of operation; and 5 min extu: 5 min after extubation. BIS values at 5 min after extubation were often missing, so no comparative analysis was conducted.</p

VAS scored at different times postoperatively.

<p>Note the VAS score at 30(p<0.01, Two-way ANOVA analysis followed by Bonferroni’s <i>post hoc</i> test). **, p<0.01, RD group <i>vs</i> HD group.</p

Patients’ characteristics.

<p>Values are presented as mean±SD RD, regular-dose group; HD, high-dose group.</p